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Topic: how to make a speed controller for a washing machine motor (Read 5551 times)

Any Whizzkids know how to make a speed controller for a washing machine motor , I want to use it as a motor on my lathe so it has to keep it's torque even at low revs . now the other thing I am a complete novice at electronics , so it has to be detailed but without "In speak "

A photo of the motor and whatever connections it has too would be helpful.....

As for assembling the mass of components, I'd suggest a pcb based one....A basic thyristor based speed controller isnt much cop because it doesnt have any feedback from the motor, so the torque suffers at low speed....not what you want...Now it starts getting complicated.

Then again what about a prebuilt speed controller? A proven design...too.I have several that are good for 6 amps( a 1200 watt motor) or some bigger ones...all are based on the KB design used in mills and lathes sold by the likes of Warco ( some endorsement huh?) these have a smallish footprint, need very little in the way of additional items to get going...( a potentiometer....)

sounds like ,I'm in the right place . Ill post some photos tomorrow .and see how we go . I kept all the panels that were in the machine don't know if any of that stuff is any good , the machine got scrapped because it was a sealed drum .and I never checked before buying a new one . and found out too late .it is possible to replace bearings in a sealed drum

Speedi - have you actually got "a naked motor" out to examine? John R's comments pertain to many motors - but some washing machines have large stepper coils - and in fact John Hill modified / re-purposed several a few years ago to power CNC router axes (third photograph down in this MadModder thread)

I think these motors are DC controlled, and if memory serves me correctly mains powered via a full wave rectifier (or at least they used to be :-)). A simple controller can be made by using the dc voltage generated by the motor rotation to trigger the thyristor when the rotation, and generated voltage falls.

Its a very simple circuit that gives excellent speed regulation vs load. The downside is that there is no mains isolation so that touching any part of the circuit could be lethal, so serious insulation and earth leakage protection mandatory.

Parts must be 400v rated (240*1.414), though the pot can be quite a high value, say 50k. Diac and thyristor to suite.

Circuit operation. Rippling DC from the full wave rectifier is fed to the Thyristor/motor series circuit. The speed control pot wiper is connected to the diac and a capacitor. When the voltage of the wiper is greater than the diac voltage plus the motor generated voltage the diac will switch to conduction and discharge the capacitor into the thyristor gate triggering it. If the motor is too fast the voltage produced will be too high to trigger.

As my old washing machine has just decided to blow up (on top of a faulty door latch which required a screwdriver and some swearing to remove one's washed clothes), I am suddenly very interested in this thread, and I'm glad it's surfaced again as I'd forgotten all about it

Just need to think of something to do with the old motor & speed controller circuit that's not a) lethal, or b) boring....

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Cheers!Ade.--Location: Wallasey, Merseyside. A long way from anywhere.Or: Zhengzhou, China. An even longer way from anywhere...Skype: adev73

A simple controller can be made by using the dc voltage generated by the motor rotation to trigger the thyristor when the rotation, and generated voltage falls.

A couple of questions... please tell me to go google it if it's easier...

What's the purpose of the 2 capacitors? I presume the large one on the RHS is to reduce ripple, and the small one between the DIAC and the pot is to negative bias the diac?Approx what size should the capacitors be?

As the pot is at up to 400v potential, presumably a boggo carbon track pot can't be used... Firstly, what component would you recommend there, and second, how hard would it be (famous last words...) to replace it with some kind of computerised pot?

Thanks!

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Cheers!Ade.--Location: Wallasey, Merseyside. A long way from anywhere.Or: Zhengzhou, China. An even longer way from anywhere...Skype: adev73

HiThe capacitor on the pot wiper is to allow a large pulse trigger current to flow when the diac voltage collapses. This means you can use thyristors with a relatively large trigger current, say up to 25mA. Larger capacitor = more trigger current. 0.1uF is good for most cases. Can also have capacitor low end connected to thyristor anode (motor side). Not a lot in it except capacitor voltage is then vdiac max say 40V - probably better to do this if you are making one. The other capacitor on the RHS is to smooth the rectified AC, and will need a voltage of 400V. 10uf is plenty, 1 uF is adequate. You can work out the ripple voltage. For a 50K pot current is around 6mA. CV=IT - near enough in this case. In the 10mS before the next pulse with 1uF 6*10-3 * 10-2 /10-6 =0.6v ripple - more than adequate in 340V (1.414*240). With a 50K pot you will need a 2W wirewound controller. There is no reason not to use a 100k pot with a 1W rating which might make things simpler.

To replace the pot with a DAC would not be difficult, but the output voltage would have to be very high so likely a simple transister buffer/amplifier would do. BF338? video deflection transistors may work for this.

Circuit speed regulation is excellent, and will allows full control from zero up to peak voltage - vdiac (~310V).

@Philf - Circuit above only gives half wave control with limited voltage swing so much less power. Do not see the need for the lower diode which appears to do nothing.

Best Regards

picclock

« Last Edit: December 19, 2016, 05:19:18 PM by picclock »

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Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

@Philf - Circuit above only gives half wave control with limited voltage swing so much less power. Do not see the need for the lower diode which appears to do nothing.

It must have been over 40 years ago that I built the last one - it worked very well giving a very good speed range. I must have binned it as my drills are now all variable speed. I worked for Mullards who then manufactured thyristors at our factory in Hazel Grove. I think it was one of our application engineers who gave me the circuit. The BT151 had a gate current of <5ma. I can't comment on the need for the diode. (I was a mechanical engineer.) I might try to cobble one together to see if it works without.

Small world - I also worked for Mullards in their New Road factory at Mitcham.

From the values shown in your drawing (by my reckoning ) the thyristor will trigger on 1/20th of the peak voltage, every half cycle, assuming the motor back emf is lower than the set point - (vtrigger +vf diode).

I would be interested to see how it performs if you make one, to see if I am mistaken about my understanding of the circuit.

Best Regards

picclock

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Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Small world - I also worked for Mullards in their New Road factory at Mitcham.

picclock

Hi Piclock,

I visited the Mitcham factory in around 1973 as well as Southampton, Blackburn (where I did my workshop training) and Simonstone. I also visited several Philips factories in Holland and France.

I think that Hazel Grove is the only one still going although no longer part of the Philips empire. They sold most of the business to a group of venture capitalists and it became NXP with Philips still having an interest. Philips then gave their share to the Pension Fund. (From which I am now benefiting!) The Hazel Grove factory is now in the process of a sale to Nexperia - a Chinese group of investors.

When I was at Blackburn (1970) they were still making valves. Around 6,000 worked there and their training school took apprentices from many other Mullard plants as well as from third party companies in the Blackburn area. Sad that it's all gone.

Yes - Southampton back in the late 1960's for my sins. Actually I learnt an awful lot from my time there - I was in the infra red devices application lab working on early multi-element arrays used in spy satellites

480 to 15000 RPM will require some serious gearing down to work on a lathe.Being a universal motor it should work through a "KB" speed controller as John Rudd Suggested.Be aware that any advice on working on mains powered equipment is at your own risk and responsibility.

Just to elaborate on my recommendation for the KB controller, there's nothing wrong with Piclocks design, its a speed controller for universal motors....But, the KB design has added features, Soft start, current limiting/overload protection and motor load feedback...All depends on how elaborate a design is needed..

The whitish blob on the back of the motor in one of your photos is a speed sensor. In the washing machine's controller which uses an IC controller this feedback is what enables it to run a steady splosh splosh splosh on the wash cycle. Worth using that if you can figure the wiring for the controller.One I played with (Hotpoint I think) wired series wound field would turn over on just 12v and got up to over 10k rpm on 70v, no load. About 20+ years ago at the ME exhibition someone showed a 12ft submarine using 2 on 24v.